A fuel cell system generates electrical power through an electrochemical reaction between a fuel gas supplied to an anode and an oxidant gas supplied to a cathode. A fuel-off gas exhausted from the anode is returned to a fuel supply flow path via a fuel circulation flow path, mixed with the fuel gas supplied from a fuel supply source, and supplied to the anode again. In the fuel cell system disclosed in Patent Document 1 below, a fuel-off gas exhausted to a fuel circulation flow path is returned to a fuel supply path using a fuel pump and an ejector, and then mixed then with a fuel gas.
Since the fuel pump circulates a fuel using electricity, while the fuel pump is able to rapidly respond to variations of a load, the power consumption increases in an operation region where efficiency is lowered. The ejector can circulate the fuel using the pressure energy of the fuel gas, but it is difficult for the ejector to respond to rapid variations of the load due to a response delay in a nozzle. In light of such circumstances, in Patent Document 1 below, the fuel cell system is provided with both a fuel pump and an ejector, so that the ejector covers an operation region where the efficiency of the fuel pump is lowered and the power consumption is increased.